Water uptake by multilayer films plays an important role in their performance. Individual layers may consist of different polymeric phases. Understanding the water uptake in such systems requires knowledge of the water distribution, its state in the polymer, and influence on the polymeric phases. This study illustrates the application of high-resolution NMR and relaxometry for measuring water distributions and evaluating water–polymer interactions. We studied water uptake in a two-layered base coat/top coat system, where the base coat consisted of acrylic, polyurethane, pigment particles, and a polymeric dispersant. Water and the polymer phases in the base coat were identified with NMR relaxometry. The water diffusivity in the base coat was determined. At high water contents water is highly mobile and is loosely bonded to the polymer. Reversible plasticization of the dispersant was observed. The polymeric dispersant seems to play a key role in the sorption of water by the coating.

The penetration of water into two-layer polymeric films of a hydrophilic base layer and hydrophobic top layer plays an important role in their performance. Little is known about the coupled effects of water uptake and stress in such films. To study such interactive phenomena, time-dependent distributions in the film are needed, which cannot be provided by traditional techniques. In this study, high-resolution NMR imaging was used to measure water profiles, showing that applied stress increased both the uptake rate and the amount of absorbed water. A model was formulated to describe the process, using the barrier properties of and the chemical potential differences over the top coat. On the basis of this, the diffusivity in the top layer and stress contribution were estimated. The results show that external stresses significantly influence water penetration into multilayer films.

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